Shoulder implant for glenoid replacement

ABSTRACT

The invention features a glenoid (shoulder socket) implant prosthesis, a humeral implant prosthesis, devices for implanting glenoid and humeral implant prostheses, and methods of their use for the treatment an injured or damaged shoulder.

FIELD OF THE INVENTION

The present invention relates to the field of total shoulderreplacement.

BACKGROUND OF THE INVENTION

The invention provides a glenoid shoulder implant, a humeral implant,and devices for preparing the glenoid and humeral head for jointreplacement.

Shoulder replacement surgery is currently used to treat patientssuffering from disabling pain due to worn or damaged shoulder joints,which can be caused by, e.g., arthritis or injury. The humeral implantscurrently in use are typically made from metal, and the implants areaffixed to the bone using bone cement (e.g., polymethylmethacrylate) orby press fitting the implant into the bone using a roughened outersurface coating on the metal for bony integration. Most glenoid(shoulder socket) implants are made completely from polyethylene andaffixed to the cortical bone using bone cement. Some glenoid implantshave a metal base plate with a polyethylene insert. Current glenoidimplants are made to sit on the surface of a reamed glenoid, which isprepared by removing any remaining cartilage and flattening the bonysurface. These implants use either a keel or multiple elongated pegs onthe back of the prosthetic glenoid implant to secure the glenoid implantinside the glenoid vault.

Keeled and pegged glenoid implants suffer from several disadvantages,which limit their lifespan once implanted and reduce the number ofindications for which they can be used when the age of the patient is afactor. For example, the glenoid implants can loosen due to poorfixation within the bone, and they are prone to wear and fatigue failureof the polyethylene due to adhesion, abrasion, and shear stress. Becauseof these deficiencies, surgeons hesitate to perform glenoid replacementsurgery on young or middle aged patients with glenoid articularcartilage injuries or damage due to early arthritis for fear that theimplant may not last more than 10-15 years in the body, thus subjectingthe patient to the possibility of two or more surgeries during thelifetime of the patient to preserve the function and pain-free state ofthe joint. Finally, current glenoid implants with a long keel or pegsare sometimes contraindicated in patients with significant glenoid boneloss. As arthritis progresses, the humeral head can wear medially anddestroy the foundation of glenoid bone. In these cases, the glenoidvault can be significantly reduced in volume and depth. Thus, a typicalkeel or peg design can broach the glenoid vault and injure thesuprascapular nerve along the suprascapular notch or spinoglenoid notchwith resultant denervation injury to the rotator cuff muscles. Broachingthrough the glenoid vault can also fracture the body of the scapula andcause early implant loosening.

There are also several disadvantages associated with current glenoidreplacement surgical techniques. Current techniques require extensiveshoulder exposure with capsular releases in order to fully expose theglenoid surface circumferentially. Since the axillary nerve is locatedwithin 1 cm of the inferior capsule, there is potential risk of axillarynerve injury with resultant denervation injury to the deltoid musclewhen these releases are performed. However, use of the current keeled orpegged glenoid implants requires this extensive glenoid exposure forproper fitting and placement. Current glenoid replacement surgery alsorequires a long skin incision and extensive soft tissue stripping inorder to fully expose the glenoid circumferentially, which produces acosmetically unappealing scar. Finally, current glenoid replacementsurgical techniques require advanced surgical training and expertisewithin the specialty of shoulder surgery, yet the majority of shoulderimplants performed in the U.S. every year are performed by orthopedicsurgeons who do not have advanced training in the subspecialty ofshoulder surgery. Therefore, many surgeons have difficulty preparing theglenoid site for a total shoulder replacement using the currenttechniques.

Because there are more than 20,000 shoulder arthoplasty surgeriesperformed per year, many U.S. patients incur a risk of continued painand disability, neuromuscular injuries, or failed shoulder prosthesesrequiring revision surgery. Thus, there remains a need for an improvedglenoid implant and improved methods for performing replacement shouldersurgery.

SUMMARY OF THE INVENTION

In one aspect, the invention features an inset glenoid shoulder implantthat is implanted within the glenoid vault, thereby allowingcircumferential cortical support along the rim of the prosthesis, whichimproves fixation strength in comparison to current glenoid implants.Another advantage of the glenoid implant is that it requires only aminimal amount of bone removal for implantation.

The glenoid implant itself includes a (1) body portion having (i) asmooth concave lateral articulating surface facing away from thescapula, which is adapted to be engaged by a convex surface of a humeralcomponent, and (ii) an opposing surface on the medial side intended tobe positioned within a cavity reamed in the glenoid. In a preferredembodiment, the glenoid implant also includes (2) a short peg on themedial side extending centrally outward along an axis from a convex orflat backside (medial) surface of the glenoid implant. In a preferredembodiment, the short peg of the glenoid implant is less than about 10mm long, more preferably about 8 mm or less in length, even morepreferably about 5 mm or less in length. Alternatively, the glenoidimplant has multiple pegs, each of which can be the same length ordifferent lengths, e.g., less than about 8 mm or less in length, morepreferably about 5 mm or less in length. In another embodiment, at leastone of the pegs is between about 5 mm and about 8 mm in length and theremaining pegs are less than about 8 mm in length.

In another preferred embodiment, the body portion extends to an edgehaving a circular configuration while, in a second embodiment, the bodyportion has an edge defining a non-circular configuration, such as anoval, an elongated configuration, or a configuration which may becharacterized as rectangular with slightly rounded ends. In anotherpreferred embodiment, the glenoid implant is implanted in a preparedcavity of the glenoid which conforms generally to the backside (medial)surface only and sits inset slightly within the glenoid vault. Inanother preferred embodiment, the glenoid implant is implanted in aprepared cavity of the glenoid which conforms generally to the singleshort peg or multiple short pegs, if present, and the backside (medial)surface of the glenoid implant.

In another preferred embodiment, the glenoid implant of the invention ismanufactured using polyethylene, metal, or ceramic, or combinationsthereof, e.g., a combination of metal and polyethylene or ceramic andpolyethylene.

In another preferred embodiment, the glenoid implant of the invention issecured to the glenoid using cement fixation or press fit technique. Inyet another preferred embodiment, the glenoid implant is further securedto the glenoid using screws, e.g., in press fit designs.

In another preferred embodiment, the glenoid implant can be customizedduring the surgical procedure, as is required based on the condition ofthe patient. In another embodiment, the glenoid implant is sterilizedprior to implantation. In yet another embodiment, the glenoid implant isprovided in sterile packaging.

In the method of implanting the glenoid component, the first step afterexposing the glenoid cavity is to determine the appropriate size ofcomponent to be used. This is done by placing a series of circularsizers having varying diameters over the glenoid cavity to determine theproper diameter to which the scapula should be reamed at the surfacedefining the glenoid cavity and the proper size of glenoid component.Using a combined sizer/guide having a central hole and passageway formedtherein to determine the correct location and attitude, a hole isdrilled a few millimeters into the scapula through the glenoid surfaceusing a combined guide wire/drill. The guide wire/drill is calibrated inorder to readily determine the depth of drilling and is attached to achuck if a power drill is used or a T-handle or the like if the drillingis manual. The guide wire/drill should be drilled into the scapulasubstantially perpendicular to the anatomic axis of the glenoid surface.Thereafter, the combined sizer/guide is removed and a reamer ispositioned to ream the scapula to the proper shape and depth forming acavity having a circular cross-sectional configuration for a circularimplant or an oval configuration for an oval implant in a plane normalto the axis defined by the guide wire.

In another aspect of the invention, the glenoid implant can be used inpatients with deficient glenoid bone due to fracture or severearthritis. In preferred embodiments, the glenoid implant has none, one,two, or three or more short backside pegs that do not extend beyondabout 10 mm outwardly from the backside (medial) surface of the glenoidimplant. In a preferred embodiment, the peg or pegs do not extend beyondabout 8 mm from the backside (medial) surface of the glenoid implant.Because the glenoid implant lacks a long backside extension, it can besafely placed inside a glenoid vault with minimal depth. This minimizesthe risk of fracturing the body of the scapula or injuring thesuprascapular nerve or rotator cuff.

Another aspect of the invention features a humeral implant for use in atotal shoulder replacement procedure. The humeral implant of the presentinvention is less than 70 mm in length, preferably about 60 mm inlength, and is less than 40 mm wide anterior to posterior (preferably 20to 30 mm wide). In an embodiment, the humeral implant includes a collar,which prevents the humeral implant from embedding too deeply in thehumerus. In other embodiment, the humeral implant includes a flange(fin), which provides fixation of the humeral implant in the medial tolateral plane and rotational control. Alternatively, the humeral implantcan contain 3 flanges (fins) with 1 lateral, 1 anterior, and 1posterior. The stem of the humeral implant defines a longitudinal axisand the planar surface extends from between about 45° to about 60° tothe axis of the stem. The proximal end of the stem includes a bore thatextends downward from the planar surface and is adapted to be engaged byan artifical humeral head by means of a morse taper. In otherembodiments, the humeral implant is fixed using a bone cement, such aspolymethylmethacrylate (PMMA) or a compatible fixation material, or itis press-fit without bone cement. The humeral implant can be customizedduring the surgical procedure, as is required based on the condition ofthe patient. In another embodiment, the humeral implant is sterilizedprior to implantation. In another embodiment, the humeral implant isprovided in sterile packaging. In another preferred embodiment, thehumeral implant of the invention is manufactured using polyethylene,metal, or ceramic, or combinations thereof, e.g., a combination of metaland polyethylene or ceramic and polyethylene.

Another aspect of the invention features a cutting jig for preparing ahumerus for replacement by a humeral implant. The humeral head cuttingjig is a simple, low profile humeral cutting jig that can be a fillcircle or part thereof. The cutting jig is placed along the anatomicneck of the humerus in the appropriate version (angle of the cut) asdetermined by the surgeon. The cutting jig can be secured along theanatomic neck of the proximal humerus using K-wires, pins, or screws andis removed after completion of humeral head resection. In an embodiment,the cutting jig includes a handle portion.

Another aspect of the invention features a method for providing ashoulder implant which can be performed through a minimal incisiontechnique (“mini-incision”). Instead of an extensive deltopectoralapproach involving extensive soft tissue stripping, capsular releases,and circumferential glenoid exposure, this inset implant can beperformed through a more limited mini-incision technique. Amini-deltopectoral incision is utilized. The skin incision is shorter,and the pectoralis tendon is left intact. The majority of the inferiorcapsule is also left intact. In a preferred embodiment, the glenoidlabrum can be left intact if this is preferred by the surgeon. Thecentral portion of the glenoid bone is then reamed while leaving theperipheral cortex intact. There are three major consequences of thismini-incision technique:

-   -   1—Shortening the length of the incision and exposure provides a        more cosmetic incision for the patient.    -   2—Avoiding an extensive inferior capule incision increases the        safety of the procedure by reducing the risk of injury to the        axillary nerve.    -   3—Providing an implant that can be placed in the glenoid without        extensive, circumferential glenoid exposure would allow general        orthopedists to perform a shoulder replacement with less        difficulty and potentially fewer complications.

The present invention is also directed to a method for implanting suchglenoid implant for precise placement in the scapula and precisedrilling and reaming of the scapula. The method is performed using aspecialized power drill having a 90 degree drilling attachment and ashort drill bit incorporated into the attachment, which is used to drilla central hole in the glenoid surface. The bone is then reamed with areamer bit attached to the drill.

Another aspect of the invention features a slim design power drill forpreparing a glenoid for implantation of a glenoid implant, in which thepower drill includes a right angle drilling attachment having anextension rod with a length of at least 10 cm, more preferably at least12, 15, or 18 cm long, the end of which is includes a collet or chuckthat is positioned at a 90° angle relative to the extension rod andwhich is adapted to receive a short drill bit; the power drill beingprepared for use in the surgical field by sterilization. In a preferredembodiment, the drill and accessories are sterilized and provided in asterile container. In other preferred embodiments, the drill bit is 10mm long, more preferably 12, 14, 16, 18, or 20 mm long, and mostpreferably 25, 35, 45, 55, 65, or 75 mm long. In other preferredembodiments, the drill bit has the following diameters: 1.5 mm, 2.5 mm,3.0 mm, 3.2 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm,8.0 mm, 9.0 mm, or 10.0 mm. The power drill is designed to allowdrilling in spaces as tight as 50 mm. In other preferred embodiments,the overall length of the right angle drilling attachment is 18 cm, morepreferably 20 cm, most preferably 22 cm. The head width and extensionrod diameter are preferably less than 25 mm, more preferably less than22 mm, and most preferably less than 20 mm. The head length ispreferably less than 30 mm, more preferably less than 28 mm, and mostpreferably less than 25 mm. In other preferred embodiments, the rightangle drilling attachment is designed to be attached to any power drill,the use of which is acceptable in a surgical field, and is designed tobe lightweight, e.g., less than about 200 grams, more preferably lessthan about 180 grams, and most preferably less than about 150 grams. Thepower drill can be powered using a battery supply (cordless) or it canbe powered using an electrical cord powered from a standard electricaloutlet. See, e.g., U.S. Pat. No. 6,037,724, incorporated herein byreference.

I have used aircraft plane drill (sioux 90 degree air angled drill; partnos. 1am 5551, 775a, and a131oah) for preparing a glenoid vault forimplantation of a glenoid implant, ensuring that the drill and bit wereproperly sterilized prior to use. Other drills are known in the art ofaircraft maintenance, once properly sterilized, are also useful in theinvention (see, e.g., item #00400; Tight Fit Tools).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an anterior surface view of the circular glenoid implant ofthe invention.

FIG. 1B is an anterior surface view of the oval glenoid implant of theinvention.

FIG. 1C is a backside view of the circular glenoid implant of FIG. 1A

FIG. 2A is an anterior surface view of the circular glenoid implant ofthe invention that includes a single short backside peg.

FIG. 2B is a backside view of the circular glenoid implant of FIG. 2B.

FIG. 3 is an anterior (frontal) view of a typical prior art glenoidimplant with a keel design situated in the glenoid.

FIG. 4 is an anterior (frontal) view of a scapula containing a typicalprior art glenoid implant with a multiple peg design situated in theglenoid.

FIG. 5 is a backside view of a scapula containing a typical prior artpegged glenoid implant which was removed from a patient.

FIG. 6 is a lateral view of the prior art pegged glenoid implant of FIG.5.

FIG. 7 is an anterior (frontal) view of a scapula containing an insetglenoid implant of the invention situated in the glenoid.

FIG. 8A is an anterior surface view of a typical prior art glenoidimplant.

FIG. 8B is an anterior surface view of the circular glenoid of theinvention.

FIG. 9A is a backside view of a typical prior art keeled glenoid trialimplant.

FIG. 9B is a backside view of the circular glenoid of the inventionshowing a short backside peg.

FIG. 10A is a surface view of the glenoid bone with an inset circularglenoid implant of the invention.

FIG. 10B is a surface view of the glenoid bone with an inset ovalglenoid implant of the invention.

FIG. 11 is a surface view of the glenoid bone with a typical prior artonlay glenoid implant, which does not sit inset to the glenoid bone.

FIG. 12 is a photograph of a model depicting the glenoid (G), scapula(S), clavicle (C), Acromio-Clavicular Joint (AC), and Coracoid (Co). Theglenoid is shaded to designate the placement surface for the glenoidimplant of the invention.

FIG. 13 is a view showing the use of a straight drill of the prior artfor preparing the glenoid for implantation.

FIG. 14 is a view of the 90° drill of the invention.

FIG. 15 is an anterior (frontal) view of the scapula showing the use ofthe 90° drill of the invention.

FIG. 16 is a view of the reamer of the invention.

FIG. 17 is frontal view of the humeral cutting jig of the invention

FIG. 18 is side view of the humeral cutting jig of FIG. 17 placed inposition on a humerus. The cutting jig can be secured by K-wires(shown), pins, or screws.

FIG. 19 is a view of the humerus and humeral cutting jig of FIG. 18after resection of humeral head along the axis of the cutting jig.

FIG. 20A is an anterior (frontal) view of the humeral implant of theinvention.

FIG. 20B is a lateral view of the humeral implant of the invention.

FIG. 20C is an anterior (frontal) view of the humeral implant of theinvention with a collar.

FIG. 20D is a lateral view of the humeral implant of the invention witha collar.

FIGS. 21, 22, and 23 are photographs showing the inset circular glenoidimplant of the invention implanted in the glenoid of a patient.

FIG. 24 is a photograph showing the 15 cm incision from a typical priorart total shoulder replacement surgery.

FIG. 25 is a photograph showing the 9 cm incision from the“mini-incision” total shoulder replacement surgery of the invention.

FIG. 26A is a view showing a right angle drill attachment for use inpreparing a glenoid for implantation of a glenoid implant.

FIG. 26B is a view showing a drill with the right angle drill attachmentand drill bits for use in preparing a glenoid for implantation of aglenoid implant.

DETAILED DESCRIPTION OF THE INVENTION

The invention features an inset glenoid implant prosthesis, a humeralimplant prosthesis, and methods and devices for preparing the surgicalsite for implantation of the implant prostheses.

The design of the glenoid implant of the invention provides increasedimplant fixation strength to glenoid bone and therefore decreases therate of glenoid implant loosening. This implant is also designed for usein cases of deficient glenoid bone which would preclude the use of acurrent glenoid implant since they require adequate bone in the glenoidvault to support multiple long pegs or a keel.

The invention also features a humeral implant, which is less than 70 mmin length, preferably about 60 mm in length, and is less than 40 mm widefrom anterior to posterior (preferably 20-30 mm). The humeral implant ofthe invention is significantly shorter and thinner (in the anterior toposterior dimension) than most current stems, which are about 70-115 mmin length and bulkier in the proximal (metaphyseal) area than distallyboth in the anterior to posterior dimension and medial to lateraldimension. Because the humeral implant of the invention is shorter, itcan be implanted in a narrower metaphyseal area and does not require theremoval of a significant amount of bone. Fixation of the present humeralimplant depends upon good interference fixation in the medial-lateralplane when press fit (similar to some current total hips). The humeralimplant can be fixed using a bone cement, such as polymethylmethacrylate(PMMA) or a compatible fixation material. Alternatively, the humeralimplant can be press-fit.

The invention also features a minimal incision shoulder arthroplastytechnique that allows replacement of the glenoid surface and humeralhead with only a small incision and less extensive soft tissuestripping. The “mini-incision” procedure also leaves the pectoralistendon and the majority of the inferior capsule intact. The glenoidlabrum can also be left intact. The central portion of the glenoid boneis then reamed while leaving the peripheral cortex intact. Theadvantages of this “mini-incision” procedure include a shorter incisionwith less scarring, increased safety, and a more simple exposure of theglenoid, thus allowing general orthopedists to perform a shoulderreplacement with less difficulty and potentially fewer complications.

The glenoid implant of the invention lacks a keel and multiple longpegs, which are typically present in the prior art glenoid implants.Instead, the glenoid implant of the invention optionally includes only asingle short (less than about 8 mm), central backside peg whichstabilizes the glenoid implant. The glenoid implant of the inventiondoes not require a long extended keel or long pegs because the majorityof the fixation strength is concentrated on the rim of the embeddedimplant. This obviates the need for significant backside fixation. Thefixation, with either cement or press fit techniques, offerscircumferential cortical bone fixation around the prosthesis. The shearstresses placed on the implant are therefore supported by acircumferential buttress of bone, which is more mechanically sound thanan onlay prosthesis with an extended backside keel or multiple longpegs.

An object of the invention is to minimize the common complications ofglenoid implant loosening and fatigue failure that exist with currentglenoid implants. All previous glenoid implants sit on the surface of areamed articular surface and utilize a keel or multiple pegs to securethe implant inside the glenoid vault (see, e.g., FIGS. 3-6). Thisinvention features a glenoid implant (which can be polyethylene, metal,ceramic, or combinations thereof) that is not designed to be placed onthe surface of the reamed glenoid articular cartilage, but rather isdesigned to be inset partially or fully within the glenoid vault (seeFIG. 7). The implant may be press fit or cemented in the reamed slotwithin the glenoid bone.

Patients who can benefit from the use of the glenoid implant of theinvention and the improved methods for performing a total shoulderarthoplasty include young, middle, and older patients with arthritis(typical total shoulder replacement (TSR) patients) or damage or injuryto the shoulder. This new inset glenoid implant allows TSR surgery fornew, previously contraindicated applications, including applications inwhich the patient presents with bone defects on the glenoid. The glenoidimplant of the invention can also be utilized in revision surgeries.

Glenoid Implant

Referring now to FIGS. 1A, 1B, and 1C, there is provided glenoid implant(10), which is intended to be implanted in the glenoid as part of a TSRarthroplasty. Glenoid implant (10) replaces the natural glenoid cavity(see G of FIG. 12) and provides a bearing surface against which the headof a humerus or humeral component may articulate. Glenoid implant (10)includes concave articulating surface (14) and convex or flat backsidesurface (16), which can, optionally, include roughened or texturedsurface (18). Glenoid implant (10) can be provided as a circular design(FIGS. 1A and 1C) or as an oblong, oval design (FIG. 1B).

Referring now to FIGS. 2A and 2B, glenoid implant (10) can includeshort, backside peg (12) on the medial, convex or flat backside surface(16) of glenoid implant (10). Short, backside peg (12) is situatedcentrally on the medial (back) side of glenoid implant (10) and ispreferably a cylindrical peg shape that extends outwardly from glenoidimplant (10) away from the back of the implant (16).

Glenoid implant (10), including or excluding short, backside peg (12),is adapted to be implanted in a prepared cavity of the glenoid (see,e.g., FIG. 12), such that it is partially or fully inset to the corticalbone of the glenoid, and is retained with bone cement or using press-fittechniques. Glenoid implant (10) can be further secured to the glenoidusing one or more screws.

Glenoid component (10) of the present invention includes concave lateralarticulating surface (14) against which the head of a humerus or humeralcomponent moves. Glenoid implant (10) is manufactured using a suitablematerial, for example, polyethylene, metal, ceramic, or combinationsthereof, with lateral articulating surface (14) being smoothlycontoured. The radius of curvature of the articulating glenoid surfacecan match the humeral head surface or it can be slightly larger than theradius of curvature of the humeral head implant.

In preferred embodiments, glenoid implant (10) has a lateralarticulating surface (14) having a concave circular or oval surfaceencircled by circular edge (20). Circular edge (20) has a thickness inthe range of about 3-6 mm, preferably about 3 mm.

The medial, back side of glenoid implant (10) is preferably roughened ortextured. For example, glenoid implant (10) can include a series ofelongated groves (18) in multiple locations for receiving bone cement toassist in the cement augmentation and retention of glenoid implant (10).

In preparing the glenoid to receive glenoid implant (10), the glenoid(G; see, e.g., FIG. 12) is reamed to receive all or a portion of glenoidimplant (10) so that glenoid implant (10) is circumferentiallysurrounded by cortical bone of the glenoid (G), which aids in thestabilization and security of glenoid implant (10).

Glenoid Drill and Reamer

Referring now to FIGS. 13-16, there will be described a method forpreparing a cavity in the glenoid for receiving a glenoid implant of thepresent invention and apparatus to be used therewith.

In preparing the cavity in the glenoid (G) to receive glenoid implant(10), the surgeon will initially determine the position of the drillsite using a guide known in the art (see, e.g., U.S. Pat. Nos.6,712,823; 6,364,910; 5,030,219; and 5,489,310; all of which areincorporated by reference).

A reamer of appropriate size is then chosen based on the size of thesizer guide previously chosen. The reamer has a symmetrical head with aplurality of cutting blades and a peripheral stop surface. Thepreviously drilled hole is used as a center guide for the reamer. Thereamer is used to create a cavity in the glenoid surface of the scapulain which the prosthetic glenoid component will be installed. After thecavity has been created, the circular or oval glenoid component isinstalled in the cavity, with or without the use of bone cement.

A method for implanting glenoid implant (10) will now be described withreference to FIGS. 13-16. Initially, if a total shoulder arthroplasty isperformed, a humeral implant having a head portion, discussed below, anda glenoid implant are implanted. Prior to implantation of the humeralcomponent into the humerus, glenoid preparation begins. With the glenoidcavity (G) of the scapula (S) exposed, an alignment or pilot hole isfirst drilled substantially in the center of the glenoid cavity (G)using, e.g., the drill shown in FIGS. 14, 15, and 26. Once the pilothole is drilled, the glenoid cavity (G) is reamed using a glenoidsurface rasp (see bit attached to the drill depicted in FIG. 16)attached to a 90° reamer shaft with driver (see FIG. 26). The glenoidsurface rasp may include a guide pin and a roughened cutting surface tocreate a trough for the glenoid component. The 90° angle of the shaft ofthe driver permits drilling in tight glenoid cavities. Thus, theprocedure can be performed in a minimally invasive manner because itdoes not require full circumferential exposure of the glenoid, nor doesit require a complete capsular release. The 90° shaft of the drillincludes a quick-connect attachment which receives the quick-connectdrill bit. The reamer is rotated by suitable power means or by hand toream the glenoid cavity. Following such reaming, the reamer and theguide wire/drill are removed leaving a cavity which is wholly containedwithin the glenoid cavity (G).

Once the holes have been drilled and the glenoid reamed, a provisionalglenoid implant may be used prior to cementing the final glenoid implantto verify hole placement, range of motion, and appropriate glenoid size,and to verify that the glenoid implant is sufficiently inset. After theproper sized glenoid implant has been selected, suitable bone cement,such as polymethylmethacrylate (PMMA) or a compatible fixation material,is placed in the reamed cavity of the glenoid vault and in the roughenedouter portions and applied to the medial (back) surface of glenoidimplant (10), if cement is to be used. Glenoid implant (10) can then bepositioned in the prepared cavity. Glenoid implant (10) is then held inplace until the cement cures to assure strong fixation of glenoidimplant (10) in the scapula. The head portion of the humerus or humeralcomponent may then engage the concave articulating surface of theglenoid implant (14).

As can be appreciated, the reaming is contained wholly within theboundary of the glenoid cavity (G) and therefore does not destroy theperipheral margin of the glenoid surface. Additionally, as can be seenin FIG. 7, there is preferably a slight overhang of glenoid implant (10)beyond the margin of the natural glenoid cavity.

This method can be performed using a deltoperctoral or anterolateralsurgical approach. For most cases, a limited deltopectoral incision willbe adequate to allow exposure to all involved structures. Use of glenoidimplant (10) in the shoulder arthroplasty procedure allows the surgeonto use a “mini-incision technique,” similar to techniques utilized fortotal knee surgery and total hip surgery.

The glenoid implant of the invention has already been implanted inseveral patients according to the patient matched implant (PMI) rulesand regulations. The implants were designed specifically for patientswith inadequate glenoid bone stock which could not support a typicalkeel or peg design.

Humeral Head Cutting Jig

Referring now to FIGS. 17-19, humeral head cutting jig (26) according tothe present invention is a simple, low profile humeral cutting jig thatcan be a full circle or part thereof. Cutting jig (26) can be secured tothe humeral head using K-wires, pins, or screws (27) and is removedafter completion of humeral head resection. Cutting jig (26) includeshandle portion (28).

The cutting jig should be placed along the anatomic neck of the humeralhead. Osteophytes which obscure the junction of the humeral head andhumeral shaft should be removed in order to accurately mark the level ofthe anatomic neck circumferentially from anterior to inferior toposterior. The cutting jig can be fixed to the humerus using wires,pins, or screws at the appropriate angle and version as determined bythe surgeon. The rotator cuff should be carefully protected withretractors, and then the humeral cut is performed using an oscillatingsaw or osteotome along the surface of the cutting jig.

The cutting jig can be manufactured using metal.

Humeral Implant

Referring now to FIGS. 20A-D, humeral implant prosthesis (38) accordingto the present invention includes stem (40) having elongated portion(42) optionally including collar (44), which prevents humeral implantprosthesis (38) from embedding too deeply in the humerus. Humeralimplant (38) also includes flange (fin) (46), which aids in the fixationof the stem in the humerus and prevents rotation of humeral implant inthe humerus. There may be just one lateral flange (fin), or there may betwo or three flanges (fins), e.g., with one lateral, one anterior, andone posterior. The stem length is preferably less than about 70 mm, andthe stem width is preferably less than about 40 mm (preferably about 30mm).

At the distal end of the stem, there is rounded portion (48) and at theproximal end of the stem is a support surface extending radially fromthe stem. The support surface has an upper planar surface (50) thatincludes bore (hole with morse taper) (52) extending inwardly from thetop plane thereof, and which is adapted to be engaged by a humeral headimplant with a morse taper extension. Modular humeral head implants(both concentric and eccentric) are known in the art (see, e.g., U.S.Pat. Nos. 4,865,605; 5,314,479; 5,462,563, and 5,489,309, and U.S.Patent Application Nos. 2004/0167629, 2004/0064187; each of which isincorporated herein by reference). The plane of upper planar surface(50) is preferably between about 45 degrees and about 60 degrees to theaxis of the stem.

The entire stem portion, or a portion thereof, is preferably coated witha porous material for aiding in the fixation of the humeral implant inthe humerus for a press fit stem. The implants made for cement fixationcan have a smooth surface or a roughened, textured surface.

Humeral implant (38) can be rectangular or rounded edges, but issignificantly thinner anterior to posterior than medial to lateral. Itwill have a morse taper for securing a standard humeral head implant.

An advantage of the humeral implant of the present invention overcurrent humeral implant stems is that the humeral implant of theinvention is significantly shorter than most current stems, which areabout 70-115 mm in length. Because the humeral implant is shorter, itsaves bone because of the narrow metaphyseal area required forimplantation. The present humeral implant is less than 70 mm in length,preferably about 60 mm in length, and less than 40 mm anterior-posteriorwidth (preferably about 30 mm). Fixation of the present humeral implantdepends upon good interference fixation in the medial-lateral plane whenpress fit (similar to some current total hips). The humeral implant canbe fixed using a bone cement, such as polymethylmethacrylate (PMMA) or acompatible fixation material, or it can be press-fit.

The invention will now be described by the following examples. Thefollowing examples are meant to illustrate the invention. They are notmeant to limit the invention in any way.

EXAMPLES Example 1

A 62 year old woman presented with progressive, debilitating shoulderpain from osteoarthritis, which she had experienced for approximately 15years. She had constant pain (rated 9/10) and difficulty washing herhair, fastening her bra, lifting a cup of coffee, and performing otherdaily activities. The preoperative radiographs and CT scan showed severeshoulder arthritis and glenoid bone loss that would preclude the use ofa keeled or pegged glenoid implant. There was concern that ahemiarthroplasty procedure (replacement of the humeral ball, which wouldleave the arthritic glenoid socket bare) would not relieve the patient'spain.

A total shoulder replacement using an inset glenoid implant of theinvention and a standard humeral implant was performed. The smaller sizeand circumferential fixation of the inset glenoid implant allowed safeplacement of the prosthesis within the confines of the patient'sdeficient glenoid cavity.

The deficient glenoid vault was not fractured and the fixation was verystable. The patient had 100% relief of pain only 1 week after surgery.Her own assessment of shoulder function 4 weeks after surgery was 56% ofnormal (American Shoulder and Elbow Society validated outcome score[ASES score]) was 56 compared to 16% of normal before the surgery (ASESscore 16).

This surgery was performed through the “mini-incision total shouldertechnique” described above. FIG. 25 shows the surgical incision 4 weekspost-operatively. FIG. 24, which shows a more typical total shoulderincision, clearly demonstrates the improved cosmetic appearance andreduced incision size achieved using the “mini-incision total shouldertechnique” described above. FIGS. 21-23 are intraoperative pictures ofthe implanted inset glenoid prosthesis in this patient.

Example 2

An 81 year old woman presented with severe shoulder pain and stiffness.She had severe shoulder arthritis with medial wear causing glenoid boneloss. Her own assessment of shoulder function was 25% of normal(American Shoulder and Elbow Society validated outcome score [ASESscore] was 25).

A total shoulder replacement using an inset glenoid implant prosthesiswas performed. Two months after her surgery, the patient had no pain andexhibited improved function. Her own assessment of shoulder function was70% of normal (American Shoulder and Elbow Society validated outcomescore [ASES score] was 70).

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications and this application is intended to cover any variations,uses, or adaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent disclosure that come within known or customary practice withinthe art to which the invention pertains and may be applied to theessential features hereinbefore set forth.

1. An inset glenoid implant comprising a body portion having (i) asmooth concave lateral articulating surface adapted to be engaged by ahumeral component, (ii) a medial surface adapted for positioning withina circular cavity reamed in the glenoid, (iii) a peripheral edge in theshape of a circle having a diameter circumferentially surrounding thebody portion, and (iv) a central peg extending coaxially from the centerof the medial surface, wherein the body in its entirety is cylindricallyshaped and, when implanted, the peripheral edge of the glenoid implantis completely circumferentially surrounded by cortical bone of theglenoid.
 2. The inset glenoid implant of claim 1, wherein said centralpeg has a length of about 8 millimeters (mm) or less.
 3. The insetglenoid implant of claim 2, wherein said peg is about 5 mm or less inlength.
 4. The inset glenoid implant of claim 1, wherein said glenoidimplant is manufactured using polyethylene, metal, ceramic, or acombination thereof.
 5. The inset glenoid implant of claim 1, whereinthe peripheral edge of said glenoid implant has a thickness of betweenabout 3 and 6 mm.
 6. The inset glenoid implant of claim 1, wherein saidglenoid implant has a roughened or textured medial side.
 7. The insetglenoid implant of claim 6, wherein said medial side comprises a seriesof elongated grooves.
 8. The inset glenoid implant of claim 1, incombination with bone cement.
 9. The inset glenoid implant of claim 8,wherein said bone cement is polymethylmethacrylate (PMMA).
 10. The insetglenoid implant of claim 1, wherein the medial surface is flat.
 11. Theinset glenoid implant of claim 1, wherein the medial surface is convex.12. The inset glenoid implant of claim 1, having bone cement adheredthereto.
 13. An inset glenoid implant comprising a body portion having(i) a smooth concave lateral articulating surface adapted to be engagedby a humeral component, (ii) a medial surface adapted for positioningwithin a circular cavity reamed in the glenoid, (iii) a peripheral edgein the shape of a circle having a diameter circumferentially surroundingthe body portion, and (iv) a peg extending from the medial surface,wherein the body as a whole is cylindrically shaped and, when implanted,the peripheral edge of the glenoid implant is completelycircumferentially surrounded by cortical bone of the glenoid.